The invention is directed to a pneumatic wheel chair cushion having a dynamic pressure relieving system for reducing ischemic injury to the weight bearing portions of the buttocks of a patient in a sitting position.
With the increasing number of wheel chair patients, the need for wheel chair cushions which provide for greater prevention of ischemic injury are needed. Typically, wheel chair cushions have been provided in various forms and shapes cut from foam. Other wheel chair cushions have been provided which include air cushions. U.S. Pat. No. 4,864,671 discloses a controllably inflated wheel chair cushion that includes a number of independently inflatable rows of cells. The cells are inflated and deflated according to a sequence selected by the user to selectively relieve pressure against the buttocks of the patient. The cells are inflated at a predetermined pressure and may not be deflated until a valve is opened to exhaust the cell. The cells are exhausted through a manifold which delivers air between the cells in order to supply fresh air and reduce the heat from the cushion. However, the system may not satisfactorily compensate a patient's weight causing excessive pressure on inflated portions. U.S. Pat. No. 4,852,195 discloses a similar fluid pressurized cushion which utilizes air cells arranged in a matrix. The air cells are inflated and deflated in a sequence to shift body support from one set of cells to another for promoting blood circulation and comfort. The cells in each matrix may also be interconnected to shift fluid pressure as the patient's weight may shift. While the above air cushions deflate to periodically alleviate pressure against the occupant's buttocks, the air cells are generally static and closed by valves and may not suitably allow pressure to be automatically relieved in instances where the patient's body weight shifts. The pressurized cushions are alternating, but are static. While the air cells or cushions are filled and pressurized with air, that pressure cannot change until the air pressure is released. This may not be satisfactory for severe cases of amputated wheel chair patients whose lower stump is very susceptible to acute ischemic injury and skin decay.
Accordingly, an object of the present invention is to provide an pneumatic wheel chair cushion having a dynamic air distribution system which periodically relieves pressure on portions of the occupant's buttocks.
Another object of the invention is to provide a pneumatic cushion having a dynamic air distribution system which is self regulating and adjusts to the shift in weight of the occupant to automatically relieve pressure and prevent ischemic injury.
Another object of the present invention is to provide a pneumatic cushion for a wheel chair and the like which utilizes individual air sacks which are inflated and deflated in a sequence to periodically reduce pressure against portions of the occupant's buttocks wherein the air sacks are controlled by a dynamic air pressurization system which allow a back flow of air to bleed from the air sacks under excessive pressure to prevent ischemic injury.
Another object of the present invention is to provide a pneumatic cushion for a wheel chair and the like which uses individual air sacks arranged in a matrix which can be alternately inflated and deflated wherein the fabric of the air sacks has a low air permeability which allows a certain amount of the air to escape to maintain the cushion dry and also to assist in automatically regulating the air pressure to shift in occupant's weight.